Method and device for transmitting and receiving channel state information in wireless communication system using multiple antennas

ABSTRACT

The present disclosure relates to a method and a device for efficiently transmitting and receiving a periodic channel state report in a wireless communication system supporting multiple antennas. The method by which a terminal transmits channel state information includes receiving control information comprising information associated with channel state reporting on a subband, receiving at least one reference signal and generating, based on the at least one reference signal, periodic channel state information comprising a first precoding matrix indicator (PMI) for a wideband, and transmitting the periodic channel state information comprising the first PMI for the wideband based on the control information associated with channel state reporting on the subband.

PRIORITY

This application is a National Phase Entry of PCT InternationalApplication No. PCT/KR2016/013374, which was filed on Nov. 18, 2016 andclaims priority to U.S. Provisional Patent Application Nos. 62/256,895,62/256,738 and 62/257,409, which were filed Nov. 18, 2015, Nov. 18, 2015and Nov. 19, 2015, respectively, the entire disclosure of each of theseapplication is incorporated herein by reference.

BACKGROUND 1. Field of the Disclosure

The present disclosure relates to methods and devices for transmittingand receiving channel state information in wireless communicationsystems, and particularly, to methods and devices for transmitting andreceiving channel state information in wireless communication systemsusing multiple antennas.

2. Description of the Related Art

In order to meet the demand for wireless data traffic soaring since the4G communication system came to the market, there are ongoing efforts todevelop enhanced 5G communication systems or pre-5G communicationsystems. For the reasons, the 5G communication system or pre-5Gcommunication system is called the beyond 4G network communicationsystem or post LTE system.

For higher data transmit rates, 5G communication systems are consideredto be implemented on ultra high frequency bands (mmWave), such as, e.g.,60 GHz. To mitigate pathloss on the ultra high frequency band andincrease the reach of radio waves, the following techniques are takeninto account for the 5G communication system: beamforming, massivemulti-input multi-output (MIMO), full dimensional MIMO (FD-MIMO), arrayantenna, analog beamforming, and large-scale antenna.

Also being developed are various technologies for the 5G communicationsystem to have an enhanced network, such as evolved or advanced smallcell, cloud radio access network (cloud RAN), ultra-dense network,device-to-device (D2D) communication, wireless backhaul, moving network,cooperative communication, coordinated multi-point (CoMP), andinterference cancellation.

There are also other various schemes under development for the 5G systemincluding, e.g., hybrid FSK and QAM modulation (FQAM) and sliding windowsuperposition coding (SWSC), which are advanced coding modulation (ACM)schemes, and filter bank multi-carrier (FBMC), non-orthogonal multipleaccess (NOMA) and sparse code multiple access (SCMA), which are advancedaccess schemes.

As such, wireless communication systems are evolving to high-speed,high-quality wireless packet data communication systems to provide dataservices and multimedia services beyond the initial versions that haveprovided voice-centered services. To that end, various standardizationorganizations, such as the 3GPP or the IEEE, proceed to standardizeevolved wireless communication systems adopting multicarrier-basedmultiple access schemes. As an example, a diversity of wirelesscommunication standards including 3GPP long term evolution (LTE) andIEEE 802.16m, have been developed to support high-rate, high-qualitywireless packet data transmission services based on multiple accessschemes. LTE, 802.16m, or other existing evolved wireless communicationsystems are based on multi-carrier multiple access schemes and mayemploy various techniques, such as the multi-antenna technology,multiple input multiple output (MIMO), beamforming, adaptive modulationand coding (AMC), and channel sensitive scheduling.

The above-enumerated techniques enhance system capability by, e.g.,concentrating transmit power coming from several antennas depending on,e.g., channel quality, adjusting the amount of data transmitted, orselectively transmitting data to the user with a relatively good channelquality to produce a better transmission efficiency. Such schemes mostlyoperate based on the channel state information between the base station(eNB or BS) and the terminal (user equipment (UE) or MS). Accordingly,it is needed to measure the channel state between the base station andthe UE. LTE systems use channel status indication reference signals(CSI-RSs) as reference signals for measuring the channel state. Basestation means a device that is located in a predetermined place to carryout downlink transmission and uplink reception. One base station mayperform transmission and reception for a plurality of cells. In awireless communication system, a plurality of base stations may begeographically dispersed and each base station may perform transmissionand reception for a plurality of cells.

The reference signal is a signal used to assist in the demodulation anddecoding of data symbols received by measuring the state of channelbetween the base station and the UE(s), such as channel strength ordistortion, interference strength, or Gaussian noise, in the wirelessmobile communication system. Another use of such a reference signal isto measure the wireless channel state. The receiver may determine thestate of radio channel between itself and the transmitter by measuringthe strength of reference signal transmitted from the transmitter at anagreed-on transmit power and received via the radio channel. Theso-determined state of radio channel is used to determine the data ratefor which the receiver is to send a request to the transmitter.

The evolved wireless mobile communication system standards such as 3GPPLTE (-A) or IEEE 802.16m primarily adopt multiple-access schemes usingmultiple subcarriers such as orthogonal frequency division multiplexing(multiple access)(A) (OFDM(A)). Wireless communication systems adoptingmultiple access schemes using multiple carriers make differences inchannel estimation and measurement capabilities depending on how manysymbols and subcarriers the reference signal they are to place in on thetime and frequency. Further, the channel estimation and measurementcapabilities are influenced by how much power is to be assigned to thereference signal as well. Accordingly, if more time, frequency, andpower or other radio resources are allocated to the reference signal,the channel estimation and measurement capability may be enhanced,resultantly leading to demodulation and decoding performance forreception data symbols, as well as increased accuracy of channel statemeasurement.

However, wireless communication systems are typically assigned limitedtime, frequency, transmit power, or other radio resources fortransmitting signals, and thus, assigning relatively many radioresources to the reference signals may relatively reduce the radioresources that may be allocated to data signals. For that reason, radioresources allocated to the reference signals should be properlydetermined considering the system throughput. In particular, a technicalfactor that matters in adopting MIMO which performs transmission andreception using multiple antennas is to assign and measure a referencesignal.

In the MIMO schemes, e.g., the full dimension (FD)-MIMO scheme, theprecoding matrix indicator (PMI) overhead that the UE should reportincreases as the codebook size goes up. In particular, periodic channelstate reporting is subject to a limitation in the size of the physicaluplink control channel (PUCCH) payload, requiring a method for reducingthe PMI overhead to fit the PUCCH payload. As an example, existingperiodic channel state reporting has adopted codebook subsampling thatremoves duplicate beam groups or reduces the co-phasing count forcompensating for the phase differences between the antennas withdifferent polarizations and beams that are selectable in order to shrinkthe codebook. However, the periodic channel state reporting that issupported by FD-MIMO bears a large PMI overhead over the existing, andadopting the existing method as it is may cause a significantperformance loss.

SUMMARY

Thus, according to the present disclosure, there are provided a methodand device for efficiently transmitting and receiving periodic channelstate reports in a wireless communication system supporting multipleantennas.

According to the present disclosure, there are also provided a methodand device capable of reducing the overhead of channel state reportingin a wireless communication system supporting multiple antennas.

According to the present disclosure, there are also provided a periodicchannel state reporting method and device capable of minimizing theperformance loss considering the increased circuit board and PMIoverhead in a wireless communication system supporting the FD-MIMO.

According to the present disclosure, there are also provided a periodicchannel state reporting method and device using a codebook defined to beadopted for various antenna arrays in a wireless communication systemsupporting the FD-MIMO.

According to an embodiment of the present disclosure, a method fortransmitting channel state information by a user equipment (UE) in awireless communication system using multiple antennas comprisesreceiving first configuration information about at least one referencesignal from a base station, receiving second configuration informationfor generating periodic channel state information based on measuring theat least one reference signal, receiving and measuring the at least onereference signal from the base station, based on the first configurationinformation, and generating the periodic channel state informationincluding a first precoding matrix indicator (PMI) for a wideband basedon the second configuration information including configurationinformation for channel state reporting on a subband and transmittingthe periodic channel state information to the base station.

According to an embodiment of the present disclosure, a UE in a wirelesscommunication system using multiple antennas comprises a transceiverconfigured to transmit and receive data and a controller configured toperform controller to receive first configuration information about atleast one reference signal from a base station, receive secondconfiguration information for generating periodic channel stateinformation based on a result of measuring the at least one referencesignal, receive and measure the at least one reference signal from thebase station, based on the first configuration information, and generatethe periodic channel state information including a first precodingmatrix indicator (PMI) for a wideband based on the second configurationinformation including configuration information for channel statereporting on a subband and transmitting the periodic channel stateinformation to the base station.

According to an embodiment of the present disclosure, a method forreceiving feedback information by a base station in a wirelesscommunication system using multiple antennas comprises transmittingfirst configuration information about at least one reference signal,transmitting second configuration information for receiving from a UE,as the feedback information, periodic channel state information based ona result of measuring the at least one reference signal, and receivingthe channel state information including a first PMI for a wideband fromthe UE based on the first configuration information and the secondconfiguration information, wherein the first PMI for the wideband isreceived from the UE based on the second configuration informationincluding configuration information for channel state reporting on asubband.

According to an embodiment of the present disclosure, a base station ina wireless communication system using multiple antennas comprises atransceiver configured to transmit and receive data and a controllerconfigured to perform control to transmit first configurationinformation about at least one reference signal, transmit secondconfiguration information for receiving from a UE, as feedbackinformation, periodic channel state information based on a result ofmeasuring the at least one reference signal, and receive the channelstate information including a first PMI for a wideband from the UE basedon the first configuration information and the second configurationinformation, wherein the first PMI for the wideband is received from theUE based on the second configuration information including configurationinformation for channel state reporting on a subband.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present disclosure will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a view illustrating an example of an FD-MIMO system usingmultiple transmit antennas;

FIG. 2 is a view illustrating an example of a radio resource that may bescheduled on a downlink in an LTE/LTE-A system;

FIG. 3 is a view illustrating the feedback timings of an RI and a wCQIin an LTE/LTE-A system;

FIG. 4 is a view illustrating the feedback timings of an RI, an sCQI,and a wCQI;

FIGS. 5 and 6 are views illustrating feedback timings where PTI=0 andPTI=1 in an LTE/LTE-A system;

FIG. 7 is a view illustrating a CSI-RS transmission method in a wirelesscommunication system using multiple antennas according to an embodimentof the present disclosure;

FIG. 8 is a view illustrating a method for channel state informationreporting in a wireless communication system using multiple antennasaccording to a first embodiment of the present disclosure;

FIG. 9 is a view illustrating a method for channel state informationreporting in a wireless communication system using multiple antennasaccording to a second embodiment of the present disclosure;

FIG. 10 is a flowchart illustrating operations of a UE according to anembodiment of the present disclosure;

FIG. 11 is a flowchart illustrating operations of a base stationaccording to an embodiment of the present disclosure;

FIG. 12 is a block diagram illustrating a configuration of a UEaccording to an embodiment of the present disclosure; and

FIG. 13 is a block diagram illustrating a configuration of a basestation according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

Hereinafter, embodiments of the present disclosure are described indetail with reference to the accompanying drawings. The same referencedenotations may be used to refer to the same or similar elementsthroughout the specification and the drawings. When making the gist ofthe present disclosure unclear, the detailed description of knownfunctions or configurations is skipped.

Other aspects, advantages, and core features of the present disclosurewill be apparent to one of ordinary skill in the art from the followingdetailed description of embodiments of the present disclosure, takeninto conjunction with the drawings.

Prior to going into the detailed description of the disclosure, it mightbe effective to define particular words and phrases as used herein. Asused herein, the terms “include” and “comprise” and their derivativesmay mean doing so without any limitations. As used herein, the term “or”may mean “and/or.” As used herein, the phrase “associated with” and“associated therewith” and their derivatives may mean “include,” “beincluded within,” “interconnect with,” “contain,” “be contained within,”“connect to or with,” “couple to or with,” “be communicable with,”“cooperate with,” “interleave,” “juxtapose,” “be proximate to, “be boundto or with, “have, or “have a property of.” As used herein, the term“controller” may mean any device, system, or part thereof controlling atleast one operation. As used herein, the term “device” may beimplemented in hardware, firmware, software, or some combinations of atleast two thereof. It should be noted that functions, whateverparticular controller is associated therewith, may be concentrated ordistributed or implemented locally or remotely. It should be appreciatedby one of ordinary skill in the art that the definitions of particularterms or phrases as used herein may be adopted for existing or future inmany cases or even though not in most cases.

For a better understanding of the present disclosure, various feedbacktransmission schemes for channel status information (CSI) in FD-MIMOsystems and LTE/LTE-A systems to which the present disclosure may beapplicable are described prior to specific embodiments of the presentdisclosure.

The present disclosure may be applied not only to FD-MIMO systems butalso, in the same or similar manner, to various wireless communicationsystems that transmit data using a few tens of, or more, antennas.

The LTE/LTE-A or other wireless communication systems utilize the MIMOtechnique in which transmission is performed using a plurality oftransmit/receive antennas in order to increase system capability anddata transmission rate. The MIMO technique makes use of a plurality oftransmission/reception antennas to spatially separate and transmit aplurality of information streams. As such, spatially separating andtransmitting a plurality of information streams is called spatialmultiplexing. Generally, the number of information streams to whichspatial multiplexing may be applied varies depending on the number ofantennas of the transmitter and receiver. In general, the number ofinformation streams to which spatial multiplexing may apply is referredto as the rank of the corresponding transmission. The MIMO techniquesupported by the LTE/LTE-A release 11 and its predecessors supportsspatial multiplexing for the case where there are eight transmissionantennas and eight reception antennas and supports up to rank-8. TheFD-MIMO system to which the technology proposed according to embodimentsof the present disclosure applies may be evolved over the existingLTE/LTE-A MIMO technology, supporting more than eight, e.g., 32 or moretransmit antennas.

The FD-MIMO system refers to a wireless communication system thattransmits data using a few tens or more transmit antennas.

FIG. 1 is a view illustrating an example of an FD-MIMO system usingmultiple transmit antennas.

Referring to FIG. 1, the base station 100 transmits wireless signalsthrough a few tends or more transmit antennas. The plurality of transmitantennas are arranged a minimum distance apart from each other asindicated by reference number 110. As an example, the minimum distanceis a half of the wavelength of the wireless signal transmitted.Generally, where the transmit antennas remain spaced at a distance whichis a half (0.5λ) of the wavelength of the wireless signal, therespective signals transmitted from the transmit antennas are influencedby radio channels that are mutually less correlated. Where the band ofthe wireless signal transmitted is 2 GHz, the minimum distance becomes7.5 cm, and if the band becomes larger than 2 GHz, this minimum distancefurther shortens.

In FIG. 1, a few tends or more transmit antennas arranged in the basestation 100 are used to transmit signals, e.g., reference numbers 120and 130, to one or more UEs. Proper precoding may be applied to theplurality of transmit antennas of the base station 100, allowing them tosimultaneously transmit signals to the plurality of UEs. At this time,one UE may receive one or more information streams. Generally, thenumber of information streams receivable by one UE is determineddepending on the channel context and the number of receive antennasowned by the UE.

In order to effectively implement the FD-MIMO system, the UE needs toexactly measure the channel context and/or interference magnitude andtransmit effective channel state information to the base station usingthe same. The base station receiving the channel state informationdetermines UEs on which it performs transmission, at what datatransmission rate to perform transmission, or the precoding to applyusing the channel state information in connection with downlinktransmission. Since the FD-MIMO system has more transmit antennas thanthe existing LTE/LTE-A system, applying the channel state information ofthe existing LTE/LTE-A system (the LTE/LTE-A system may simply bereferred to as LTE system unless stated otherwise) to the FD-MIMO systemmay cause the uplink overhead issue that massive control informationshould be td on the uplink.

The wireless communication system has limited time, frequency, and powerresources. Thus, if more resources are allocated to the referencesignal, the resources allocable for traffic channel (data trafficchannel) transmission may be reduced, thus resulting in a decrease onthe absolute amount of data transmitted. In such case, the channelmeasurement and estimation capability may be enhanced, but since theabsolute amount of data transmitted is reduced, the overall systemcapability may be rather lowered. Accordingly, a proper distribution isrequired between resources for the reference signal and resources forsignals for traffic channel transmission in order to bring up with theoptimal performance from a point of view of the overall systemcapability.

FIG. 2 illustrates an example of a radio resource schedulable on thedownlink in an LTE/LTE-A system, wherein the minimum unit of the radioresource, i.e., one subframe and one resource block (RB), is shown.

The radio resource shown in FIG. 2 is constituted of one subframe 200including a control region 215 and a data region 220 on the time axisand one RB on the frequency axis. Such a radio resource includes, e.g.,12 subcarriers 210 in the frequency domain and 14 OFDM symbols 205 inthe time domain, totaling 168 unique frequencies and time positions. Inthe LTE/LTE-A system, each frequency and time position corresponding toone subcarrier and one symbol section is referred to as a resourceelement (RE) 225.

The LTE system may transmit a plurality of different types of signals inthe radio resource shown in FIG. 2 as follows.

Cell specific RS (CRS) 230: a reference signal that is periodicallytransmitted for all the UEs belonging to one cell and that may be sharedby a plurality of UEs.

Demodulation reference signal (DMRS) 235: a reference signal transmittedfor a particular UE. This signal is transmitted only when data istransmitted to the corresponding UE. A DMRS may consist of a total ofeight DMRS ports. In LTE/LTE-A, port 7 to port 14 correspond to DMRSports, and the ports maintains orthogonality not to interfere with eachother using code division multiplexing (CDM) or frequency divisionmultiplexing (FDM).

Physical downlink shared channel (PDSCH) 240: a data channel transmittedon the downlink, used for a base station to transmit traffic to a UE,and transmitted via an RE where no reference signal is transmitted inthe data region of FIG. 2.

Channel status information reference signal (CSI-RS) 250: a referencesignal transmitted for UEs belonging to one cell and used to measure thechannel state. A plurality of CSI-RSs may be transmitted in one cell.

Other control channels (PHICH, PCFICH, and PDCCH) 245: provide controlinformation necessary for the UE to receive the PDSCH or transmit theACK/NACK to operate the hybrid automatic repeat and request (HARD) foruplink data transmission.

Besides the signals, the LTE-A system may set a muting so that CSI-RStransmitted from another base station may be received withoutinterfering with the UEs in the cell. The muting may apply in theposition where the CSI-RS may be transmitted. Generally, the UE may skipthe corresponding radio resource, where the CSI-RS is transmitted, andmay receive a traffic signal. The muting in the LTE-A system is alsocalled zero-power CSI-RS. This is why the muting applies likewise to theresource positions of the CSI-RS and no transmit power is transmitted.

Referring to FIG. 2, the CSI-RS may be transmitted using some of thepositions denoted with A, B, C, D, E, E, F, G, H, I, and J depending onthe number of antennas transmitting the CSI-RS. Further, the muting mayalso apply to some of the positions denoted with A, B, C, D, E, E, F, G,H, I, and J. In particular, the CSI-RS may be transmitted via two, four,or eight REs depending on the number of antenna ports. In case thenumber of antenna ports is two, the CSI-RS is transmitted through a halfof a particular pattern of FIG. 2, in case the number of antenna portsis four, the CSI-RS is transmitted through the overall particularpattern, and in case the number of antenna ports is eight, the CSI-RS istransmitted via two patterns. By contrast, the muting is carried outalways through each pattern. That is, the muting, although applicable toa plurality of patterns, cannot apply to only part of one pattern in thecase where it does not overlap the position of the CSI-RS. However, onlyif the muting overlaps at position the CSI-RS, it may apply only to partof one pattern.

Where the CSI-RS is transmitted over two antenna ports, the CSI-RStransmits the respective signals of the antenna ports in two REsconnected together on the time axis, and the respective signals of theantenna ports are distinguished by orthogonal codes. Further, where theCSI-RS is transmitted for four antenna ports, two REs are added to theCSI-RS for two antenna ports, so that signals for the two antenna portsare further transmitted by the same method. The same also applies wherethe CSI-RS is transmitted for eight antenna ports.

Generally, the wireless communication system needs to transmit areference signal to measure the state of the downlink channel. In the3GPP LTE-advanced (LTE-A) system, the UE may measure the channel statebetween the UE and the base station using the CRS or CSI-RS that thebase station transmits. Basically, some factors should be considered forthe channel state, e.g., the quantity of interference on the downlink.The interference quantity on the downlink includes interference signalsor thermal noise that is caused by the antennas in the neighbor basestation and this is critical for the UE to determine the channel contextof the downlink. As an example, where the base station using onetransmit antenna transmits signals to the UE using one receive antenna,the UE determines per-symbol energy receivable on the downlink using thereference signal received from the base station and the amount ofinterference to be simultaneously received in the period where thesymbol is received and determines the signal-to-noise ratio (e.g.,Es/Io). The determined Es/Io is converted into a data transmission speedor its corresponding value and is notified to the base station in theform of a CQI, thereby enabling determination as to the datatransmission speed at which the base station should perform datatransmission to the UE on downlink.

In the LTE-A system, the UE feedbacks information about the channelstate of the downlink to the base station so that it may be utilized fordownlink scheduling by the base station. That is, the UE measures thereference signal transmitted from the base station on downlink andfeedbacks the information extracted therefrom to the base station in aform as defined in the LTE-LTE-A standards. The information fed back bythe UE in the LTE/LTE-A system includes three types of information (RI,PMI, and CQI) as follows:

1) Rank indicator (RI): the number of spatial layers that may bereceived in the current channel state by the UE

2) Precoder matrix indicator (PMI): an indicator for a precoding matrixfavored by the UE in the current channel state.

3) Channel quality indicator (CQI): a maximum data rate at which the UEmay perform reception in the current channel state. The CQI may bereplaced with the signal-to-noise ratio (SINR), maximum error correctioncode rate and modulation scheme, or data efficiency per frequency whichmay be utilized similar to the maximum data rate.

The RI, PMI, and CQI are associated with one another and have meanings.Different precoding matrices as supported in the LTE/LTE-A system aredefined per rank as an example. Accordingly, the PMI value Y when the RIis 1 and the PMI value Y when the RI is 2 are interpreted differently,for example. Further, it is assumed that when the UE determines the CQI,the PMI value, Y, that the UE has provided to the base station has alsoapplied. That is, the UE feedbacking the RI_X, PMI_Y, and CQI_Z to thebase station is the same as the UE notifying the base station that datamay be received at the data transmission rate corresponding to the CQI_Zwhen the rank is the RI_X and the precoding is the PMI_Y. As such, theUE may assume the transmission scheme that the base station is toperform when calculating the CQI so that the optimized performance canbe achieved when the base station actually performs transmission in thetransmission scheme.

In the LTE/LTE-A system, the UE's periodic feedback information is setto one of the following four feedback modes (or reporting modes)depending on what information is contained:

1) Reporting mode 1-0: RI, wideband CQI (hereinafter, wCQI)

2) Reporting mode 1-1: RI, wCQI, PMI

3) Reporting mode 2-0: RI, wCQI, subband CQI (hereinafter, sCQI)

4) Reporting mode 2-1: RI, wCQI, sCQI, PMI

The feedback timing of each piece of information for the four feedbackmodes is determined by values transferred by a higher layer signal, suchas N_(pd), N_(OFFSET,CQI), M_(R1), and N_(OFFSET,R1). Here, N_(pd) andN_(OFFSET,CQI) mean the period and offset value in the subframes forCQI/PMI reporting, and M_(R1) and N_(OFFSET,R1) means the period andrelative offset value in the subframes for RI reporting. In feedbackmode 1-0, the transmission period of wCQI is N_(Pd), and the feedbacktiming is determined with the subframe offset of N_(OFFSET,CQI).Further, the transmission period of RI is N_(Pd)×M_(R1), and thesubframe offset is N_(OFFSET,CQI)+N_(OFFSET,R1)

FIG. 3 is a view illustrating the feedback timings of the RI and wCQI inthe LTE/LTE-A system, e.g., the feedback timings of the RI 305 and thewCQI 310 where N_(pd)=2, M_(R1)=2, N_(OFFSET,CQI)=1, andN_(OFFSET,R1)=−1. In FIG. 3, each timing (0, 1, . . . , 20, . . . )denotes a subframe index.

Feedback mode 1-1, although having the same feedback timing as feedbackmode 1-0, differs in that the PMI together with the wCQI 310 istransmitted at the wCQI transmission timing as shown in FIG. 3.

Meanwhile, in feedback mode 2-0, the feedback transmission period forthe sCQI is N_(pd), and the offset value is N_(OFFSET,CQI), and thefeedback transmission period for the wCQI is fix H×N_(pd), and theoffset value is N_(OFFSET,CQI) as is the offset value of the sCQI. Here,H=J*H+1, where K is a value transferred through the higher layer signal,and J is a value determined depending on the system bandwidth. Forexample, for 10 MHz systems, J may be defined as 3. At last, the wCQI istransmitted once for every H sCQI transmissions. The transmission of theRI is M_(R1)×H×N_(pd), and the offset is N_(OFFSET,CQI)+N_(OFFSET,R1).

FIG. 4 is a view illustrating the feedback timings of the RI, sCQI, andwCQI, e.g., the feedback timings of the RI 405, wCQI 410, and sCQI 415where N_(pd)=2, M_(R1)=2, J=3(10 MHz), K=1, N_(OFFSET,CQI)=1, andN_(OFFSET,R1)=−1. In FIG. 4, each timing (0, 1, . . . , 20, . . . )denotes a subframe index.

Feedback mode 2-1, although having the same feedback timing as feedbackmode 2-0, differs in that the PMI together with the wCQI 410 istransmitted at the wCQI transmission timing as shown in FIG. 4.

In FIGS. 3 and 4, the above-described feedback timing is for the casewhere the number of CSI-RS antenna ports is four or less, and for the UEreceiving allocation of CSI-RS for other partial four or eight antennaports, two types of PMI information should be fed back unlike thefeedback timing.

Specifically, for eight CSI-RS antenna ports, feedback mode 1-1 isdivided again into two submodes. In the first submode, the RI togetherwith the first PMI information is transmitted, and the second PMIinformation is transmitted together with the wCQI. Here, the feedbackperiod and offset for the wCQI and the second PMI are defined as N_(pd)and N_(OFFSET,CQI), and the feedback period and offset for the RI andthe first PMI are defined as M_(R1)×N_(pd) andN_(OFFSET,CQI)+N_(OFFSET,R1). Here, assuming that the precoding matrixcorresponding to the first PMI is W1 (or W₁), and the precoding matrixcorresponding to the second PMI is W2 (or W₂), the UE and the basestation share the information that the UE's favored precoding matriceshave been determined as W1 and W2.

In the case of feedback mode 2-1 for eight CSI-RS antenna ports, thefeedback of precoding type indicator (PTI) information is added. The PTIis fed back along with the RI, the period is M_(R1)×H×N_(pd), and theoffset is defined as N_(OFFSET,CQI)+N_(OFFSET,R1). Where the PTI is 0,the first PMI, the second PMI, and the wCQI are all fed back, and thewCQI and the second PMI are together transmitted in the same timing, andthe period is N_(pd), and the offset is given as N_(OFFSET,CQI).Further, the period of the first PMI is H′×N_(pd), and the offset isN_(OFFSET,CQI). Here, H′ is transferred through a higher layer signal.Further, where PTI is 1, PTI together with RI is transmitted, and wCQIand the second PMI are transmitted together, and sCQI is fed back at anadditional separate timing. In this case, the first PMI is nottransmitted. The period and offset of the PTI and RI are the same asthose where the PTI is 0, and the period and offset of the sCQI aredefined as N_(pd) and N_(OFFSET,CQI). Further, the wCQI and the secondPMI are fed back in the period of H×N_(pd) and the offset ofN_(OFFSET,CQI), and H is defined like the number of CSI-RS antenna portsis four.

FIGS. 5 and 6 are views illustrating feedback timings where PTI=0 andwhere PTI=1, respectively, in the LTE/LTE-A system, wherein whereN_(pd)=2, M_(R1)=2, J=3(10 MHz). K=1, H′=3, N_(OFFSET,CQI)=1,N_(OFFSET,R1)=−1, and PTI=0 (FIG. 5) and PTI=1 (FIG. 6), FIG. 5illustrates the feedback timings of the RI and PTI 505, the first PMI(PMI1) 510, and the second PMI (PMI2) and the wCQI 515, and FIG. 6illustrates the feedback timings of the RI and PTI 605, the wCQI andwPMI2 610, and the sCQI/sPMI2 615. In FIG. 6, the wPMI2 means the secondPMI for the wideband, and the sPMI2 means the second PMI for thesubband. In FIGS. 5 and 6, each timing (0, 1, . . . , 20, . . . )denotes a subframe index.

The LTE/LTE-A system supports the UE's aperiodic feedback transmissionas well as the periodic feedback transmission. When the base stationdesires to obtain aperiodic feedback information of a particular UE, thebase station sets the aperiodic feedback indicator included in thedownlink control information (DCI, downlink control information) foruplink data scheduling of the UE to perform particular aperiodicfeedback and performs the uplink data scheduling of the UE. Thecorresponding UE, when receiving the indicator set to perform aperiodicfeedback transmission in an nth subframe, includes the aperiodicfeedback information upon data transmission in an n+kth subframe andperforms uplink transmission. Here, k is a parameter defined in the 3GPPLTE release 11 standards, and this is 4 for frequency division duplexing(FDD) while defined as shown in Table 1 for time division duplexing(TDD). Table 1 below represents an example of k for each subframe numbern in the TDD UL/DL configuration.

TABLE 1 TDD UL/DL subframe number n Configuration 0 1 2 3 4 5 6 7 8 9 0— — 6 7 4 — — 6 7 4 1 — — 6 4 — — — 6 4 — 2 — — 4 — — — — 4 — — 3 — — 44 4 — — — — — 4 — — 4 4 — — — — — — 5 — — 4 — — — — — — — 6 — — 7 7 5 —— 7 7 —

Where the aperiodic feedback transmission is set, the feedbackinformation includes RI, PMI, and CQI like in the case of the periodicfeedback transmission, and the RI and the PMI might not be fed backaccording to feedback settings. The CQI may include both the wCQI andthe sCQI or only the wCQI information.

The LTE/LTE-A system provides codebook sampling functionality forperiodic channel state reporting. In the LTE/LTE-A system, the periodicfeedback transmission of the UE is transmitted to the base stationthrough the PUCCH. Since the amount of information that may betransmitted once through PUCCH is limited, various feedback objects,such as RI, wCQI, sCQI, wPMI2, and sPMI2, may be transmitted throughPUCCH by way of subsampling or two or more pieces of feedbackinformation may be encoded together (joint encoding) and may betransmitted through PUCCH. As an example, when eight CSI-RS ports areconfigured by the base station, RI and PMI1 reported in submode 1 ofPUCCH mode 1-1 may be joint-encoded as shown in Table 2. PMI1constituted of 4 bits and RI constituted of 3 bits based on Table 2 arejoint-encoded with a total of five bits. Submode 2 of PUCCH mode 1-1joint encodes PMI1 consisting of four bits and PMI2 consisting of otherfour bits as shown in Table 3 into four bits in total. Since submode 2has a higher subsampling level than submode 1 (e.g., four bits=>threebits subsampling in the case of submode 1, and eight bits=>four bitssubsampling in the case of submode 2), it cannot report more precodingindexes. As such, subsampling means reducing the number of informationbits and transmitting the information. As another example, where eightCSI-RS ports are configured by the base station, PMI2 reported in PUCCHmode 2-1 may be subsampled as shown in Table 4 below. Referring to Table4, PMI2, when its associated RI is 1, is reported with four bits.However, in case the associated RI is two or more, differential CQI forthe second codeword should be reported together, and thus it may be seenthat PMI2 is subsampled with two bits and reported. The LTE/LTE-A systemmay apply subsampling or joint encoding to six types of periodicfeedback in total including Tables 2, 3, and 4. Table 2 below representsan example of joint encoding on a first codebook index (ii) and the RIfor submode 1 of PUCCH mode 1-1.

TABLE 2 Value of joint encoding of RI and the first PMI I_(RI/PMI1) RICodebook index i₁ 0-7 1 2I_(RI/PMI1)  8-15 2 2(I_(RI/PMI1) − 8)  16-17 32(I_(RI/PMI1) − 16) 18-19 4 2(I_(RI/PMI1) − 18) 20-21 5 2(I_(RI/PMI1) −20) 22-23 6 2(I_(RI/PMI1) − 22) 24-25 7 2(I_(RI/PMI1) − 24) 26 8 0 27-31reserved NA

Table 3 below represents an example of joint encoding on the first andsecond codebook indexes (i₁, i₂) and the RI for submode 2 of PUCCH mode1-1.

TABLE 3 Relationship between the Relationship between the first PMIvalue and second PMI value and codebook index i₁ codebook index i₂ Valueof the Value of the first PMI Codebook second PMI Codebook total RII_(PMI1) index i₁ I_(PMI2) index i₂ #bits 1 0-7 2I_(PMI1) 0-1 2I_(PMI2) 4 2 0-7 2I_(PMI1) 0-1 I_(PMI2) 4 3 0-1 2I_(PMI1) 0-7 4 └I_(PMI2)/4┘ +I_(PMI2) 4 4 0-1 2I_(PMI1) 0-7 I_(PMI2) 4 5 0-3  I_(PMI1) 0 0 2 6 0-3 I_(PMI1) 0 0 2 7 0-3  I_(PMI1) 0 0 2 8 0 0 0 0 0

Table 4 represents an example of codebook subsampling for PUCCH mode2-1.

TABLE 4 Relationship between the second PMI value and codebook index i₂Value of the Codebook RI second PMI I_(PMI2) index i₂ 1  0-15  I_(PMI2)2 0-3 2I_(PMI2) 3 0-3 8 · └I_(PMI2)/2┘ + (I_(PMI2) mod 2) + 2 4 0-32I_(PMI2) 5 0 0 6 0 0 7 0 0 8 0 0

As described above, in order to effectively implement the FD-MIMOsystem, the UE needs to exactly measure the channel state andinterference magnitude and generate and report effective channel stateinformation to the base station using the same. The base stationreceiving the channel state information determines UEs on which itperforms transmission, at what data transmission rate to performtransmission, or the precoding to apply using the channel stateinformation in connection with downlink transmission. The FD-MIMO systemhas many transmit antennas and considers a two-dimensional antennaarray, and the shape of the antenna array actually applicable theretomay be very diversified. Accordingly, it is not appropriate to apply themethod for transmitting and receiving channel state information for theLTE/LTE-A system, which is designed considering only a one-dimensionaltransmit antenna array having up to eight antennas, to the FD-MIMOsystem as it is. To optimize the FD-MIMO system, it is necessary todefine a new codebook that is applicable to diverse antenna arrayshapes.

To that end, according to embodiments of the present disclosuredescribed below, there are proposed schemes for reducing the complexityin channel state reporting corresponding to multiple dimensions, such asthe vertical and horizontal dimension or the first and seconddimensions, in periodic channel state reporting by allowing the PMI tobe transmitted using the existing 2, 4, or 8 CSI-RS port codebook andsome of the CSI-RSs configured for the plurality of CSI-RS ports toreduce the overhead and design complexity upon PMI reporting using atwo-dimensional (2D) codebook in the FD-MIMO-based transmission andreception that is based in the LTE-A system.

Generally, where multiple transmit antennas are used as is the FD-MIMOsystem, CSI-RS s should be transmitted in proportion thereto. As anexample, where the LTE/LTE-A system uses eight transmit antennas, thebase station transmits the CSI-RS corresponding to eight ports to the UEand allows it to measure the channel state of the downlink. At thistime, the base station may use a radio resource constituted of eight REssuch as As and Bs in FIG. 2 in one RB in transmitting the CSI-RScorresponding to the eight ports. Applying the CSI-RS transmission ofthe LTE/LTE-A system to the FD-MIMO system requires that the radioresource proportional to the number of transmit antennas be allocated tothe CSI-RS. That is, where the base station has 128 transmit antennas,the base station transmits the CSI-RS using a total of 128 REs in oneRB. Such CSI-RS transmission scheme may raise the accuracy of channelmeasurement between antennas but requires excessive radio resources andthus may reduce radio resources necessary to transmit and receivewireless data. Accordingly, given such merits and demerits, thefollowing two methods may be considered upon transmission of the CSI-RSin the base station adopting multiple transmit antennas such as in theFD-MIMO system.

CSI-RS transmission method 1: a method of performing transmission, withas many radio resources as the number of antennas assigned to the CSI-RS

CSI-RS transmission method 2: a method of performing transmission, withthe CSI-RS divided into a plurality of dimensions.

FIG. 7 is a view illustrating a CSI-RS transmission method in a wirelesscommunication system using multiple antennas according to an embodimentof the present disclosure. CSI-RS transmission methods 1 and 2 aredescribed with reference to FIG. 7.

Referring to FIG. 7, the FD-MIMO operating base station may takeadvantage of a few tens of (e.g., a total of 32 or more) multipleantennas. Reference number 300 in FIG. 7 denotes a method of assigningas many radio resources as the number of antennas and performingtransmission using CSI-RS transmission method 1. In reference number300, 32 antennas, respectively, are marked with A0, . . . ,A3, B0, . . .,B3, C0, . . . ,C3, D0, . . . ,D3, E0, . . . ,E3, F0, . . . ,F3, G0,. .. ,G3, H0, . . . ,H3. In reference number 300, the 32 antennas maytransmit two-dimensional (2D) CSI-RSs, and the 2D-CSI-RSs which enablemeasurement of the channel state of all the horizontal and verticalantennas may be transmitted through the 32 antenna ports marked asabove. Such method may raise the accuracy of channel information becauseeach antenna is assigned a radio resource but consumes relative moreradio resources for control information or data, and is thus noteffective in terms of resource efficiency.

Reference number 310 in FIG. 7 is a method enabling the UE to performchannel measurement on many transmit antennas while allocating arelatively small number of radio resources even if it presents arelatively low accuracy of channel state information using CSI-RStransmission method 2. This is an example of the method in which allCSI-RSs are separated into N dimensions and transmitted. For example,where the transmit antennas of the base station are arrayed in 2D asshown in FIG. 1, the CSI-RSs are separated into two dimensions andtransmitted. At this time, the first (dimensional) CSI-RSs are operatedas horizontal CSI-RSs for measuring the channel state of the horizontaldirection, and the second (dimensional) CSI-RSs are operated as verticalcameras for measuring the channel state of the vertical direction. Inthe example of FIG. 7, the 32 antennas in reference number 310,respectively, are marked with A0, . . . ,A3, B0, . . . ,B3, C0, . . .,C3, D0, . . . ,D3, E0, . . . ,E3, F0, . . . ,F3, G0, . . . ,G3, H0, . .. ,H3, like in reference number 300. As such, in the example of FIG. 3,the 32 antennas may transmit the first and second CSI-RSs correspondingto the two dimensions in the horizontal and vertical directions. At thistime, the H-CSI-RS for measuring the channel state of the horizontaldirection may be transmitted through the following eight antenna portsas in reference number 320.

H-CSI-RS port 0: is configured of a combination of antennas A0, A1, A2,and A3

H-CSI-RS port 1: is configured of a combination of antennas B0, B1, B2,and B3

H-CSI-RS port 2: is configured of a combination of antennas C0, C1, C2,and C3

H-CSI-RS port 3: is configured of a combination of antennas D0, D1, D2,and D3

H-CSI-RS port 4: is configured of a combination of antennas E0, E1, E2,and E3

H-CSI-RS port 5: is configured of a combination of antennas F0, F1, F2,and F3

H-CSI-RS port 6: is configured of a combination of antennas G0, G1, G2,and G3

H-CSI-RS port 7: is configured of a combination of antennas H0, H1, H2,and H3

In the above embodiment, combining a plurality of antennas into oneCSI-RS port means antenna virtualization which may typically be achievedby a linear combination of the plurality of antennas. The V-CSI-RS formeasuring the channel state of the vertical direction may be transmittedthrough the following four antenna ports as in reference number 330.

V-CSI-RS port 0: is configured of a combination of antennas A0, B0, C0,D0, E0, F0, G0, and H0

V-CSI-RS port 1: is configured of a combination of antennas A1, B1, C1,D1, E1, F1, G1, and H1

V-CSI-RS port 2: is configured of a combination of antennas A2, B2, C2,D2, E2, F2, G2, and H2

V-CSI-RS port 3: is configured of a combination of antennas A3, B3, C3,D3, E3, F3, G3, and H3

As such, where a plurality of antennas are arrayed in 2D, e.g., by M×N(vertical direction x horizontal direction), the channel state in theFD-MIMO system may be measured using the N horizontal CSI-RS ports andthe M vertical CSI-RS ports. That is, where two CSI-RSs are used, thechannel state may be grasped using M+N CSI-RS ports for MN transmitantennas. As such, grasping the information on more transmit antennasusing fewer CSI-RS ports acts as a critical advantage in reducing CSI-RSoverhead. In the above embodiment, MN=K CSI-RSs are used to grasp thechannel state for the transmit antennas in the FD-MIMO system, and suchapproach may apply likewise where two CSI-RSs are used. Although theembodiment of the present disclosure described assumes the use of CSI-RStransmission method 1, the above approach may apply likewise whereCSI-RS transmission method 2 is used.

As in the above example, the existing 2, 4, or 8 port CSI-RSs may bebundled up for the CSI-RS port to support multiple antennas. Such CSI-RSport supporting method may be varied depending on whether to use thenon-precoded (NP) CSI-RS in which the CSI-RS is transmitted in the samescheme as the existing 2, 4, or 8 port CSI-RS or to use the beamformed(BF) CSI-RS in which the CSI-RS overhead has been reduced by applyingbeamforming to the antennas. To support the NP CSI-RS and the BF CSI-RS,the CSI-RS resources or CSI-RS port positions for existing 1, 2, 4, or 8CSI-RS ports may be bundled up using the RRC fields shown in Tables 5 to11. Although the information shown in Tables 5 to 11 is separately setforth for convenience purposes, the information shown in Tables 5 to 11may also be appreciated as one connected RRC field. That is, Tables 5 to11 represent examples of configurations of CSI-process information andCSI-RS information for NP CSI-RS and BF CSI-RS transmission.

TABLE 5 -- ASN1START CSI-Process-r11 ::= SEQUENCE { csi-ProcessId-r11CSI-ProcessId-r11, csi-RS-ConfigNZPId-r11 CSI-RS-ConfigNZPId-r11,csi-IM-ConfigId-r11 CSI-IM-ConfigId-r11, p-C-AndCBSRList-r11 SEQUENCE(SIZE (1..2)) OF P-C-AndCBSR- r11, cqi-ReportBothProc-r11CQI-ReportBothProc-r11 OPTIONAL, -- Need OR cqi-ReportPeriodicProcId-r11INTEGER (0..maxCQI-ProcExt- r11) OPTIONAL, -- Need ORcqi-ReportAperiodicProc-r11 CQI-ReportAperiodicProc-r11 OPTIONAL, --Need OR ...,

TABLE 6 [[ alternativeCodebookEnabledFor4TXProc-r12 ENUMERATED {true}OPTIONAL, -- Need ON csi-IM-ConfigIdList-r12 CHOICE { release NULL,setup SEQUENCE (SIZE (1..2)) OF CSI-IM-ConfigId-r12 } OPTIONAL, -- NeedON cqi-ReportAperiodicProc2-r12 CHOICE { release NULL, setup CQI-ReportAperiodicProc-r11 } OPTIONAL -- Need ON ]], [[ eMIMO-Type-r13CHOICE { release NULL, setup CHOICE { nonPrecoded-r13NonPrecodedCSI-RS-Info-r13, beamformed-r13 BeamformedCSI-RS-Info-r13 }OPTIONAL } OPTIONAL -- Need ON ]] }

TABLE 7 P-C-AndCBSR-r11 ::= SEQUENCE { p-C-r11 INTEGER (−8..15),codebookSubsetRestriction-r11 BIT STRING } P-C-AndCBSR-r13 ::= SEQUENCE{ p-C-r11 INTEGER (−8..15), codebookSubsetRestriction1-r13 BIT STRING,ccdebookSubsetRestriction2-r13 BIT STRING OPTIONAL, -- Cond NonPreCodedcodebookSubsetRestriction3-r13 BIT STRING OPTIONAL -- Cond Beamformed }

TABLE 8 P-C-AndCBSR-PerResourceConfig-r13 ::= SEQUENCE (SIZE (1..2))P-C- AndCBSR-r13 NonPrecodedCSI-RS-Info-r13 SEQUENCE {p-C-AndCBSRList-r13 SEQUENCE (SIZE (1..2)) P-C-AndCBSR-r13,codebookConfigN1-r13 ENUMERATED {an1, an2, an3, an4, an8},codebookConfigN2-r13 ENUMERATED {an1, an2, an3, an4, an8},codebookOverSamplingRateConfig-O1-r13 ENUMERATED {N/A,4,8},codebookOverSamplingRateConfig-O2-r13 ENUMERATED {N/A,4,8},codebookSubsetSelectionConfig-r13 ENUMERATED {1, 2, 3, 4} }

TABLE 9 BeamformedCSI-RS-Info-r13 SEQUENCE {csi-RS-ConfigNZPIdListExt-r13 SEQUENCE (SIZE (1..7)) OFCSI-RS-ConfigNZPId-11, csi-IM-ConfigIdListExt-r13 SEQUENCE (SIZE (1..7))OF CSI-IM-ConfigId-r11, p-C-AndCBSR-PerResourceConfigList-r13 SEQUENCE(SIZE (1..4)) OF P-C-AndCBSR-PerResourceConfig-r13 OPTIONAL -- Need OR,} -- ASN1STOP

TABLE 10 -- ASN1START CSI-RS-ConfigNZP-r11 ::= SEQUENCE {csi-RS-ConfigNZPId-r11 CSI-RS-ConfigNZPId-r11, antennaPortsCount-r11ENUMERATED {an1, an2, an4, an8}, resourceConfig-r11 INTEGER (0..31),subframeConfig-r11 INTEGER (0..154), scramblingIdentity-r11 INTEGER(0..503), qcl-CRS-Info-r11 SEQUENCE { qcl-ScramblingIdentity-r11 INTEGER(0..503), crs-PortsCount-r11 ENUMERATED {n1, n2, n4, sparel},mbsfn-SubframeConfigList-r11 CHOICE { release NULL, setup SEQUENCE {subframeConfigList MBSFN-SubframeConfigList } } OPTIONAL -- Need ON }OPTIONAL, -- Need OR ... [[ eMIMO-Info-r13 CHOICE { release NULL, setupSEQUENCE { nzp-resourceConfigList-r13 SEQUENCE (SIZE (2..8)) OFResourceConfig-r13, cdmType ENUMERATED {cdm2, cdm4} OPTIONAL -- Need OR} } OPTIONAL, -- Need ON ]] }

TABLE 11 ResourceConfig-r13 ::= INTEGER (0...31) MeasRestrict-Config::=SEQUENCE { eMIMO-InfoBeamformed CHOICE { release NULL, setup SEQUENCE {channelMeasRestriction ENUMERATED {on} //only for Class B// ,interferenceMeasRestriction ENUMERATED {on} //mandatory both for Class Aand Class B// } -- ASN1STOP

The NP CSI-RS may support 12, 16, or more CSI-RS ports using thepositions for the existing CSI-RS in one subframe and using theinformation (e.g., RRC field) of Tables 5 to 11. To that end, the fieldinformation is set forth as nzp-resourceConfigList-r13 in Tables 5 to11, and the field information may be used to set the position for theCSI-RS. Further, in the BF CSI-RS, csi-RS-ConfigNZPldListExt-r13 andcsi-IM-ConfigIdListExt-r13 may be used to bundle up individual CSI-RSresources which may differ in the number of CSI-RS ports, subframe, andcodebook subset restriction to be used as the BF CSI-RS. To support 2Dantennas in the NP CSI-RS, a new 2D codebook is required which may bevaried depending on per-dimension antennas and oversampling factors andcodebook settings.

The terms as used herein are defined as follows.

RI: a rank indicator that has been reported from the UE to the basestation for the rank of channel obtained by simultaneously applyinghorizontal and vertical precodings to the 2D-CSI-RS or that has beendetermined by a predetermined rule

i₁: a first PMI (i.e., corresponding to Wi) that the UE has notified thebase station by obtaining the optimal precoding based on the channelobtained by applying 2D precoding to the 2D-CSI-RS. The first PMI mayindicate a beam group selected in the horizontal and verticaldirections.

i₁₁: a beam group selected in the first dimension for the 2D-CSI-RS.This may be some bits of the first PMI bit payload (Wi bit payload).

i₁₂: a beam group selected in the second dimension for the 2D-CSI-RS.This may be some bits of the first PMI bit payload (Wi bit payload).

i₂: a second PMI (i.e., corresponding to W₂) that the UE has notifiedthe base station by obtaining the optimal precoding based on the channelobtained by applying 2D precoding to the 2D-CSI-RS. The second PMI mayindicate co-phrasing necessary to correct the phase difference betweenantennas with different polarizations and the beam selected from thebeam group selected in the horizontal and vertical directions.

CQI: corresponds to the data transmission rate that the UE may supportas generated under the assumption that 2D precoding has simultaneouslyapplied.

The structure of the 2D codebook may be represented as in Equation 1below.

W 632 (W ₁₁ ⊗W ₁₂)W ₂ =W ₁ W ₂  [Equation 1]

Here, W₁₁ and W₁₂ indicate the PMIs related to some bits of the firstPMI bit payload (W1 bit payload) and are respectively selected by i₁₁and i₁₂. In this case, Equation 1 may be directly represented in thecodebook and thus be shown or may indirectly be represented. W2 is alsoselected by i₂ that indicates the second PMI as does Tables 12 and 13below exemplify the rank1 2D codebook using such a 2D codebookstructure, representing an example of the 2D codebook for 1-layer CSIreporting.

TABLE 12 • The PMI feedback payload is adjusted based on Config - Config= 1 (compact i₂, no beam selection for 1 and 2 layers): • # of bits fori₁₁ and i₁₂ = ceil(log₂(N₁O₁)) + ceil(log₂(N₂O₂)) • # of bits for i₂(per rank 1,2) = (2,2) - Config = 2, 3, 4 (following legacy): • # ofbits for i₁₁ and i₁₂ = ceil(log₂(N₁O_(I)/2))+ ceil(log₂(N₂O₂/2)) • # ofbits for i₂ (per rank 1,2) = (4,4) - TBD rank 3-8

TABLE 13 i₂′ 0 1 2 3 Precoder W_(s) ₁ _(i) _(1,1) _(,s) ₂ _(i) _(1,2)_(,0) ⁽¹⁾ W_(s) ₁ _(i) _(1,1) _(,s) ₂ _(i) _(1,2) _(,1) ⁽¹⁾ W_(s) ₁ _(i)_(1,1) _(,s) ₂ _(i) _(1,2) _(,2) ⁽¹⁾ W_(s) ₁ _(i) _(1,1) _(,s) ₂ _(i)_(1,2) _(,3) ⁽¹⁾ i₂′ 4 5 6 7 Precoder W_(s) ₁ _(i) _(1,1) _(+1,s) ₂ _(i)_(1,2) _(,0) ⁽¹⁾ W_(s) ₁ _(i) _(1,1) _(+1,s) ₂ _(i) _(1,2) _(,1) ⁽¹⁾W_(s) ₁ _(i) _(1,1) _(+1,s) ₂ _(i) _(1,2) _(,2) ⁽¹⁾ W_(s) ₁ _(i) _(1,1)_(+1,s) ₂ _(i) _(1,2) _(,3) ⁽¹⁾ i₂′ 8 9 10 11 Precoder W_(s) ₁ _(i)_(1,1) _(+2,s) ₂ _(i) _(1,2) _(,0) ⁽¹⁾ W_(s) ₁ _(i) _(1,1) _(+2,s) ₂_(i) _(1,2) _(,1) ⁽¹⁾ W_(s) ₁ _(i) _(1,1) _(+2,s) ₂ _(i) _(1,2) _(,2)⁽¹⁾ W_(s) ₁ _(i) _(1,1) _(+2,s) ₂ _(i) _(1,2) _(,3) ⁽¹⁾ i₂′ 12 13 14 15Precoder W_(s) ₁ _(i) _(1,1) _(+3,s) ₂ _(i) _(1,2) _(,0) ⁽¹⁾ W_(s) ₁_(i) _(1,1) _(+3,s) ₂ _(i) _(1,2) _(,1) ⁽¹⁾ W_(s) ₁ _(i) _(1,1) _(+3,s)₂ _(i) _(1,2) _(,2) ⁽¹⁾ W_(s) ₁ _(i) _(1,1) _(+3,s) ₂ _(i) _(1,2) _(,3)⁽¹⁾ i₂′ 16-31 Precoder Entries 16-31 constructed with replacing thesecond subscript s₂i_(1,2) with s₂i_(1,2) + 1 in entries 0-15 ConfigSelected i₂′ indices (s₁, s₂)

Config 1 0-3 (1, 1)

Config 2 0-7, 16-23 (2, 2)

Config 3 0-3, 8-11, 20-23, 28-31 (2, 2)

Config 4 0-15 (2, 2) Oversampling factors o_(d)$W_{m_{1},{m_{2}n}}^{(1)} = {\frac{1}{\sqrt{Q}}\begin{bmatrix}{v_{m_{1}} \otimes u_{m_{2}}} \\{\phi_{n}{v_{m_{1}} \otimes u_{m_{2}}}}\end{bmatrix}}$ Beam group spacing: s_(d) $v_{m_{1}} = \begin{bmatrix}1 & e^{j\frac{2\pi \; m_{1}}{o_{1}N_{1}}} & \ldots & e^{j\frac{2\pi \; {m_{1}{({N_{1} - 1})}}}{o_{1}N_{1}}}\end{bmatrix}^{t}$ First PMI: i_(1,d) $u_{m_{2}} = \begin{bmatrix}1 & e^{j\frac{2\pi \; m_{2}}{o_{2}N_{2}}} & \ldots & e^{j\frac{2\pi \; {m_{2}{({N_{2} - 1})}}}{o_{2}N_{2}}}\end{bmatrix}^{t}$

In Table 12 above, configuration parameters necessary for PMI reporting,N1, N2, O1, O2 config, may adopt those set forth in Tables 5 to 11,i.e., codebookConfigN1-r13, codebookConfigN2-r13,codebookOverSamplingRateConfig-O1-r13,codebookOverSamplingRateConfig-O2-r13, andcodebookSubsetSelectionConfig-r13. The following embodiments of thepresent disclosure propose schemes for supporting periodic channel statereporting based on a plurality of CSI-RS ports and codebooks. N1 and N2mean the numbers of antennas per dimension, and O1 and O2 meanoversampling factors per dimension.

First Embodiment

In order to support periodic channel state information reporting basedon the 2D codebook, existing subband channel state reporting may expandto wideband and subband reporting.

FIG. 8 is a view illustrating a method for channel state informationreporting in a wireless communication system using multiple antennasaccording to the first embodiment of the present disclosure, where thefeedback timings of the RI 805, i₁₁/i₁₂ 810, and i₁₂/CQI 815 are shown.

An analysis of the PMI bits of the 2D codebook reveals that, for thesecond PMI, i.e., i₂(W₂), reporting, the existing channel statereporting method is available with 4 bits or less. However, in the caseof 810 related to some bits of the first PMI bit payload (W1 bitpayload), the PMI bits increase, as follows, for the configurationparameters, N1, N2, O1, O2, and Config, supported for PMI reporting asshown in Tables 14 and 16. Tables 14 and 16 represent examples of PMIoverhead of the 2D codebook.

TABLE 14 (N1, N2) (O1, O2) combinations (8, 1) (4, —), (8, —) (2, 2) (4,4), (8, 8) (2, 3) {(8, 4), (8, 8)} (3, 2) {(8, 4), (4, 4)} (2, 4) {(8,4), (8, 8)} (4, 2) {(8, 4), (4, 4)}

TABLE 15 Config = 1 (N1, N2) (O1, O2) W₁₁/W₁₂ bits (O1, O2) W₁₁/W₁₂ bits(8, 1)  (4, —) 5 bits  (8, —) 6 bits (2, 2) (4, 4) 3 bits/3 bits (8, 8)4 bits/4 bits (2, 3) (8, 4) 4 bits/4 bits (8, 8) 4 bits/5 bits (3, 2)(8, 4) 5 bits/3 bits (4, 4) 4 bits/3 bits (2, 4) (8, 4) 4 bits/4 bits(8, 8) 4 bits/5 bits (4, 2) (8, 4) 5 bits/3 bits (4, 4) 4 bits/3 bits

TABLE 16 Config = 2, 3, 4 (N1, N2) (O1, O2) W₁₁/W₁₂ bits (O1, O2)W₁₁/W₁₂ bits (8, 1)  (4, —) 4 bits  (8, —) 5 bits (2, 2) (4, 4) 2 bits/2bits (8, 8) 3 bits/3 bits (2, 3) (8, 4) 3 bits/3 bits (8, 8) 3 bits/4bits (3, 2) (8, 4) 4 bits/2 bits (4, 4) 3 bits/2 bits (2, 4) (8, 4) 3bits/3 bits (8, 8) 3 bits/4 bits (4, 2) (8, 4) 4 bits/2 bits (4, 4) 3bits/2 bits

In the case of PUCCH format 2 which is used for existing periodicchannel state information reporting, 11 bits may be transmitted in thenormal CP context. Further, in the case of the bits for transmission ofW₁₁/W₁₂ which is the PMI related to some bits of the first PMI bitpayload (W₁ bit payload), the sum of the two (W₁₁,W₁₂) does not exceed11 bits. Accordingly, according to an embodiment of the presentdisclosure, the amount of payload data required for periodic channelstate information reporting may be reduced by applying the existing CSIreporting instance used in the subband described in connection withFIGS. 5 and 6 (i.e., the RRC information used in the subband) to thewideband (i.e., by applying the same to the first PMI reporting asdenoted with reference number 810 of FIG. 8). The reporting time at thistime may be the same as that described above in connection with FIGS. 5and 6.

Applying this method of the present disclosure enables no or minimumapplication of the subsampling, which may deteriorate performance,thereby allowing for periodic channel state information reporting.Accordingly, as in the embodiment of FIG. 8, the overhead issue with theperiodic channel state information reporting may be addressed byapplying separate wideband PMI reporting periods for i₁₁/i₁₂ forW₁₁/W₁₂. Such embodiment of the present disclosure may likewise applythe subband CSI reporting structure mentioned in connection with FIGS. 5and 6 and may use the periodic configuration field shown in Table 17 asin the existing subband CSI reporting. Table 17 below representsexamples of period configuration fields related to the PMI overhead ofthe 2D codebook.

TABLE 17 cqi-FormatIndicatorPeriodic-r10 CHOICE { widebandCQI-r10SEQUENCE { csi-ReportMode-r10 ENUMERATED {submode1, submode2} OPTIONAL-- Need OR }, subbandCQI-r10 SEQUENCE { k INTEGER (1..4),periodicityFactor-r10 ENUMERATED {n2, n4} } },

In Table 17 above, k and periodicityFactor-r10 are fields forconfiguring the wideband PMI reporting period when PTI=1 or 0.periodicityFactor-r10 is intended for setting the wideband PMI(W1)reporting period when PTI=0 (wideband information reporting), and k is afield for determining the subband reporting period on the subband, afterwhich the wideband information reporting is to be carried out.

The following are methods for setting the channel state reporting timeusing the method of the first embodiment.

Reporting time setting method 1: sets in the same manner as existingones used on the subband.

Reporting time setting method 2: is a brand-new method.

Reporting time setting method 1 uses the same scheme as existing onesused on the subband. In this case, RI reporting may be represented as inEquation 2.

(10×n _(f) +└n _(S)/2┘−N _(OFFSET,CQI) −N _(OFFSET,R1))mod(H·N _(pd) ·M_(R1))=0, H=J·K+1  [Equation 2]

In Equation 2, J is the number of bandwidth parts, and K is the same ask mentioned above and this is a value to allow the RI to be reportedevery k times the subband reporting period n_(f) is the subframe number,and ns is the slot number. Such RI reporting time is set same on thewideband and subband, and a difference from the existing reportingscheme is that k and the bandwidth part value based on the downlinkbandwidth may also be used for wideband reporting. In this case, thereporting time for the wideband first PMI may also be represented as inEquation 3 in the same way as the existing one used on the subband.

(10×n _(j) +└n _(S)/2┘−N _(OFFSET,CQI))mod(H′·N _(pd))=0,H′=periodicityFactor  [Equation 3]

The wideband second PMI/wideband CQI reporting may be represented as inEquation 4.

(10×n _(f) +└n _(S)/2┘−N _(OFFSET,CQI))modN _(pd)=0  [Equation 4]

Accordingly, where the fields mentioned in connection with FIG. 8 areused for wideband CSI reporting in reporting time setting method 1,periodicityFactor-r10 may be used, and where it is used for subband CSIreporting, k and periodicityFactor-r10 may be used. In the case of fourtransmit antennas (4Tx) and eight transmit antennas (8Tx), the UE mayselect wideband and subband reporting using the PTI. In the case ofwideband reporting (PTI=O), the above equation may be used. Subbandreporting (PTI=1 or not reported, in the case of 2Tx) may use theexisting equation on the subband as follows. The RI reporting time isthe same as that in the wideband reporting, and this and Equation 5below may be used to report the wideband PMI and wideband CQI (orwideband second PMI and wideband CQI) in the subband reporting.

(10×n _(f) +└n _(S)/2┘−N _(OFFSET,CQI))mod(H·N _(pd))=0  [Equation 5]

Further, the reporting time for the subband CQI and subband second PMImay be represented as in Equation 6 below.

(10×n _(f) +└n _(S)/2┘−N _(OFFSET,CQI))modN _(pd)=0  [Equation 6]

Reporting time setting method 2 may freely set reporting times unlikethe existing method. Where wideband CSI reporting is supported using thefirst embodiment, the reporting time need not be associated with thenumber of bandwidth parts unlike in the existing scheme, ensuring morefreedom. Accordingly, the reporting time may be defined by adopting newparameters for wideband first PMI and RI reporting. For descriptionpurposes, the values may be assumed as MRI and Md. The parameters may bereferred to with various denotations, such as P_(RI), P_(i1), M_(w1), H,and K, and they, if supporting the same operations, may be the samedespite different denotations. The parameters may be particular valuespre-defined in the standards or may be set by RRC signaling. At thistime, the following are methods for setting the RI reporting period.

RI reporting period setting method 1: sets as a multiple of the CQIperiod.

RI reporting period setting method 2: sets as a multiple of the widebandPMI period.

RI reporting period setting method 1 is a method of setting as amultiple of the CQI period.

In this case, the wideband PMI period is irrelevant to the RI period. Inthis case, the corresponding reporting time may be represented as inEquation 7.

(10×n ₁ +└n _(S)/2┘−N _(OFFSET,CQI) −N _(OFFSET,RI))mod(N _(pd) ·N_(R1))=0  [Equation 7]

In Equation 7, N_(pd) and N_(OFFSET,CQI) mean the period and offsetvalue in the subframes for CQi/PMI reporting, and M_(R1) andN_(OFFSET,R1) and means the period and relative offset value in thesubframes for RI reporting.

As above, the RI reporting period and the offset are set based on theCQI reporting period, thereby allowing the RI reporting time to be set.

RI reporting period setting method 2 is a method of setting as amultiple of the wideband PMI period. In this case, the correspondingreporting time may be represented as in Equation 8.

(10×n ₁ +└n _(S)/2┘−N _(OFFSET,CQI) −N _(OFFSET,R1))mod(M _(i1) ·N _(pd)·M _(R1))=0  [Equation 8]

In this case, the period of the wideband PMI is set as a multiple of theCQI reporting period, and the RI reporting period is set as a multipleof the same. Accordingly, the RI reporting period and offset may be setand the RI reporting time may be set. At this time, the reporting timeof the wideband PMI is shown in Equation 9.

(10×n ₁ +└n _(S)/2┘−N _(OFFSET,CQI))mod(M_(i1) ·N _(pd))=0  [Equation 9]

As set forth above, the reporting time of the wideband PMI is a multipleof the period, and the offset may not be considered. However, anadditional offset may be considered in which case the offset should bereflected to the RI reporting time.

In the above method, since the subband channel state reporting alreadysupports the corresponding structure, it may be proper to limit theabove-described method to use only for the wideband channel statereporting. Accordingly, a method that may be considered is to set thesame k and periodicity Factor as the existing ones for subband reportingwhile setting new parameters for wideband reporting. Further, the MM maybe the same parameter as the MRI supported in the existing standards.

To support the above-described first embodiment, subband CSI reportingrequires additional information to report the subband position, andthus, additional subsampling may be considered for reporting for W2. Forsuch subsampling, new different subsampling may be designed and appliedper Config or the existing method may be reused. Further, subsamplingmay be reused only for partial channel state reporting corresponding tosome Configs, e.g., Configs. 2, 3, and 4. This is why Config1 has arelatively small i2 size and is less necessary to apply sub sampling to.Accordingly, in the instant embodiment, the existing codebook subsampling may be reused, and to that end, examples of table informationare shown in Tables 18 and 19.

Table 18 represents an example of codebook subsampling for eighttransmit antennas, and Table 19 represents an example of codebooksubsampling for four transmit antennas.

TABLE 18 Relationship between the second PMI value and codebook index i₂ Value of the Codebook RI second PMI I_(PMI2) index i₂ 1  0-15 I_(PMI2) 2 0-3 2I_(PMI2) 3 0-3 8 · └I_(PMI2)/2┘ + (I_(PMI2) mod 2) + 24 0-3 2I_(PMI2) 5 0 0 6 0 0 7 0 0 8 0 0

TABLE 19 Relationship between the second PMI value and codebook index i₂Value of the Codebook RI second PMI I_(PMI2) index i₂ 1  0-15 I_(PMI2) 20-3  I_(PMI2) + 2 · └I_(PMI2)/2┘ 3 0-3 2I_(PMI2) + 4 · └I_(PMI2)/2┘ 40-3 2I_(PMI2) + 4 · └I_(PMI2)/2┘

Second Embodiment

The second embodiment is directed to a method for supporting periodicchannel state reporting using one of CSI-RS resources supported for theNP CSI-RS. As set forth in Tables 5 to 11, the NP CSI-RS may support 12,16, or more CSI-RS ports using the positions for the existing CSI-RSs inone subframe. The corresponding field is represented asnzp-resourceConfigList-r13 which may be used to set the position for theCSI-RS. Such supporting method is a method for bounding up a pluralityof CSI-RS ports to support 12, 16, or more similar CSI-RSs. At thistime, such a method is also available as to support the periodic channelstate reporting only on a particular CSI-RS resource by designating theCSI-RS resource so as to reduce the overhead of the periodic channelstate reporting.

FIG. 9 is a view illustrating a method for channel state informationreporting in a wireless communication system using multiple antennasaccording to a second embodiment of the present disclosure, showing anexample of channel state report transmission based on, e.g., 16 portCSI-RSs or 8 port CSI-RSs as denoted with reference numbers 905 and 910.

For aperiodic channel state reporting, the UE measures the channel onall the CSI-RS ports to determine the RI/PMI/CQI and transmits them tothe base station. At this time, although the use of the method proposedin the first embodiment is advantageously able to support more precodingto enhance performance, it may increase the reporting instances,resulting in additional consumption of resources and period.Accordingly, it may support more than eight CSI-RS ports by using thechannel state reporting and codebook supported in the existing 2, 4, and8 CSI-RS ports. At this time, since the wideband uses smaller reportinginstances, more reporting may be done in the context where the UE is inhigher mobility, and the uplink resources may be consumed less and maythus be used for other uplink transmissions. Further, for the resourcesused for periodic channel state reporting, the CSI-RSs may betransmitted only through the corresponding resources, and powerconsumption may thus be reduced. Further, the number of codebookssupported in the 2, 4, or 8 CSI-RS ports is relatively small, and thusthe UE becomes less complicated. At this time, the following methods areused to designate the corresponding CSI-RS resource.

CSI-RS resource designating method 1: uses the first resource set forthe RRC in periodic channel state reporting

CSI-RS resource designating method 2: puts an additional field in theRRC field to set what resource is to be used in periodic channel statereporting.

CSI-RS resource designating method 1 is a method for indirectly settingthe CSI-RS resource to be used in periodic channel state reporting wherethe base station sets the CSI-RS resource using the RRC field set forthin Tables 5 to 11. In this case, no additional overhead is needed, andthus, the UE may be subject to less complexity in implementation.

CSI-RS resource designating method 2 is a method for allowing the basestation to directly set on what CSI-RS resource is to be used forperiodic channel state reporting. CSI-RS resource designating method 2may present different optimal CSI-RS positions depending on contexts,advantageously allowing for flexible use depending on contexts.

Further, the above method may lose accuracy where less CSI-RS ports areset. For example, where two CSI-RS ports are set, only four codebooksare supported for rank 1. Accordingly, in such case, the performance mayencounter a problem.

In the case of four ports, the LTE system supports two codebooks. Onesupports only 16 PMIs, the enhanced codebook supports up to 256, and thecorresponding is used using 16 first (wideband) PMIs and second(subband) PMIs. Supporting more PMIs delivers a better performance.Thus, having more CSI-RS ports allows for use of an enhanced codebookwhen the 4-port codebook is based. Accordingly, using the 4-portcodebook using the method proposed in the second embodiment may supporta higher performance when always using the enhanced codebook. In thiscase, to support the corresponding operation, the UE may ensure the useof always using the enhanced 4Tx codebook where 4 port channel statereporting is performed for 12 or 16 port CSI-RS channel state reporting.

Third Embodiment

The third embodiment is directed to a method of using the existing 4 or8 Tx codebooks by combining the CSI-RS ports as set. As mentioned above,the 2Tx codebook may lose freedom or accuracy to support 12 or 16 CSI-RSports or multiple similar CSI-RS ports. Accordingly, in such case, theperformance may encounter a problem. However, supporting 12, 16, or moresimilar CSI-RS ports using the 2 port CSI-RSs enables the position ofthe CSI-RS port to be more flexibly set, advantageously allowing forvarious settings given the mobility and accuracy or the CSI-RS transmitpower. Thus, such method, although able to secure enough flexibility andpower, is always based on the 2Tx codebook in periodic channel statereporting even in the case of 12 or 16 CSI-RS ports. Therefore, in suchcase, it is also possible to combine and use the resources. Variousmethods as follow may be used in such combining.

Combining method 1: combines and uses with respect to the CSI-RS portindex

Combining method 2: includes and uses until the number for reporting ismet, starting with the first one

Combining method 3: sets the corresponding resource using the RRC field.

Combining method 1 above is a method for combining with respect to theCSI-RS port index. In the LTE standards, the CSI-RS ports may be indexedwith port indexes 15, 16, . . . , 30. At this time, upon reporting theperiodic channel state information using the 8Tx codebooks, the CSI-RSports corresponding to 15, . . . , 22 may be used for periodic channelstate reporting.

Combining method 2 above is a method for combining and using withrespect to the resource index. As mentioned above, the CSI-RS positionresource indexes are set to the fields 0, 1, . . . , 7, respectively.Accordingly, where 8 Tx codebooks are supported for the 2 port CSI-RSports, four 2 CSI-RS ports should be supported. Accordingly, periodicchannel state reporting is supported using the corresponding number 0,1, 2, and 3 resources. To determine the index of the resource, such amethod may also be available to use 0, 1, 2, . . . fornzp-resourceConfigList-r13 depending on preset order.

Combining method 3 is a method of setting the corresponding resourceusing the RRC field. At this time, the bitmap may also be one method.For example, where 16 CSI-RS ports are supported using two CSI-RS ports,eight CSI-RS resources are needed. Accordingly, a method available inthis case is to use eight bitmaps. For example, assuming that 11001100is set, a bundle into eight ports may be made using the numbers 0, 1, 4,and 5 CSI-RS resources, thereby able to report the channel stateinformation.

As mentioned above in the above combining method, a need exists for amethod for setting the number of CSI-RS ports corresponding to thecodebooks. The following methods may be available as the above methods.

Port count setting method 1: directly sets in the RRC field

Port count setting method 2: sets with respect to the maximum number ofCSI-RS ports supported in the corresponding CSI-RS ports

Port count setting method 3: sets using the number defined in thestandards.

Port count setting method 1 is a method of directly setting in the RRCfield. The use of this method renders it possible to directly set in theRRC field how many CSI-RS ports are to be set in the periodic channelstate reporting. For example, a field, such as CSI-RS ports Periodic,may be left in the RRC field, and a number may be set in thecorresponding field. The number set at this time may be 2, 4, or 8.

Port count setting method 2 is a method of setting depending on themaximum number of CSI-RS ports supported in the corresponding CSI-RSports. For example, 16 ports may be set using eight 2 CSI-RS ports ortwo 8 CSI-RS ports. In such case, since the maximum number of individualCSI-RS resources settable is 8, although 2 CSI-RS ports are used,reporting should be made always using 8. Taking 12 ports as an example,they may be set using three 4 CSI-RS ports and six 2 CSI-RS ports. Inthis case, thus, even though it is for 2 CSI-RS ports, reporting may berendered to be done based on 4 CSI-RS ports.

Further, in the third embodiment, like the second embodiment, the methodof always applying the 4 CSI-RS ports may likewise apply to ensure theperiodic channel state reporting performance.

Fourth Embodiment

The first to third embodiments have their own merits and demerits.Accordingly, it is also possible to support the corresponding periodicchannel state reports as submodes. An example method is to support thesecond or third embodiment in the case of submode 1 and the firstembodiment in the case of submode2. Such method enables a selection asto whether to allow the base station to use the channel state reportwhile supporting more accurate precoding or to use a shorter period andlower power while supporting less accurate precoding.

Fifth Embodiment

The second embodiment and the third embodiment may be selectivelyapplied depending on contexts. For example, it may be varied dependingon whether the RE position of the CSI-RS to support multiple CSI-RSports is eight ports or two ports. Where 16 ports are supported usingtwo 8 port CSI-RSs and eight 2 port CSI-RSs, since one 8 port CSI-RS isenough to support eight ports, periodic channel state information may begenerated using the same. Accordingly, in this case, the periodicchannel state report may be generated using the second embodiment.However, in the case of supporting using eight 2 port CSI-RSs, theaccuracy of the channel state information or the quantization level maybe insufficient. Accordingly, in this case, aggregation may be performedwith respect to the port index or resource index using the thirdembodiment so that the periodic channel state is reported using the 8Txcodebooks, addressing such problem. 12 ports may also be set using three4 port CSI-RSs and six 2 port CSI-RSs in which case aggregation may beperformed with respect to the port index or resource index among the six2 port CSI-RSs, and the periodic channel state is reported using the 4Txcodebooks, addressing such problem.

FIG. 10 is a flowchart illustrating operations of a UE according to anembodiment of the present disclosure.

Referring to FIG. 10, the UE receives configuration information aboutthe CSI-RS configuration in step 1010. Further, the UE may identify,based on the received configuration information, at least one of thenumber of ports for each NP CSI-RS, N1 and N2, which are the numbers ofantennas per dimension, O1 and O2, which are oversampling factors perdimension, a plurality of resource configs for setting one subframeconfig and position for transmitting multiple CSI-RSs, codebook subsetrestriction-related information, CSI reporting-related information,CSI-process index, and transmit power information. Thereafter, the UEreceives one feedback configuration information based on at least one 2,4, or 8 port CSI-RS position in step 1020. In the feedback configurationinformation, the PMI/CQI period and offset, RI period and offset,whether wideband/subband, and submode may be set. In step 1030, uponreceiving multiple CSI-RSs in one subframe based on the feedbackconfiguration information, the UE estimates the channel between the basestation antenna and the UE's receive antenna based on the CSI-RSs. Instep 1040, the UE generates at least one of the rank, PMI, and CQI asfeedback information using the received feedback configurationinformation based on a virtual channel added between the estimatedchannel and the CSI-RS. At this time, at least one of the methodsproposed according to the above-described embodiments of the presentdisclosure may be used to generate the corresponding feedbackinformation. That is, more than one of the plurality of embodiments ofthe present disclosure may be considered together, and which may beachieved by the submode setting. Thereafter, the UE may transmit thefeedback information to the base station at a feedback timing determinedbased on the feedback configuration of the base station in step 1050 andcomplete the process of generating and reporting the channel feedbackconsidering the two-dimensional arrangement. At least one of the methodssuggested based on the embodiments of the present disclosure may beapplied to the feedback timing at this time.

FIG. 11 is a flowchart illustrating operations of a base stationaccording to an embodiment of the present disclosure.

Referring to FIG. 11, the base station transmits, to the UE,configuration information for the CSI-RS to measure the channel state onthe UE in step 1110. The configuration information about the CSI-RS mayinclude at least one of the number of ports for each NP CSI-RS, N1 andN2, which are the numbers of antennas per dimension, O1 and O2, whichare oversampling factors per dimension, a plurality of resource configsfor setting one subframe config and position for transmitting multipleCSI-RS s, codebook subset restriction-related information, CSIreporting-related information, CSI-process index, and transmit powerinformation. Thereafter, the base station transmits to the UE feedbackconfiguration information based on at least one CSI-RS in step 1120. Inthe feedback configuration information, at least one of the PMI/CQIperiod and offset, RI period and offset, whether wideband/subband, andsubmode may be set. Thereafter, the base station transmits the CSI-RSconfigured based on the configuration information about the CSI-RS tothe UE. Then, the UE estimates the channel state per antenna port,estimates an additional channel state for the virtual resource based onthe estimated channel state, and generates feedback information forchannel state reporting. At this time, one of the embodiments proposedherein may be used to generate the corresponding feedback information,and multiple ones of the embodiments of the present disclosure maytogether be considered which may be achieved by the submode setting. TheUE generates feedback information including at least one of the PMI, RI,and CQI as above and transmits the feedback information to the basestation. Accordingly, the base station receives the feedback informationfrom the UE at a predetermined feedback timing and uses the same todetermine the channel state between the UE and the base station in step1130.

FIG. 12 is a block diagram illustrating a configuration of a UEaccording to an embodiment of the present disclosure.

Referring to FIG. 12, the UE includes a transceiver 1210 and acontroller 1220. The transceiver 1210 performs the function oftransmitting or receiving data to/from another network entity (e.g., abase station). Here, the transceiver 1210 may generate the feedbackinformation under the control of the controller 1220 and transmit thefeedback information to the base station. The controller 1220 controlsthe state and operation of all the components of the UE to generate andtransmit feedback information based on at least one of the embodimentsof the present disclosure set forth above. Specifically, the controller1220 generates feedback information according to the informationallocated by the base station. Further, the controller 1220 controls thetransceiver 1210 to feedback the generated channel information to thebase station according to the timing information allocated by the basestation. To that end, the controller 1220 may include a channelestimator 1230. The channel estimator 1230 determines necessary feedbackinformation through the feedback configuration information and theCSI-RS received from the base station and estimates the channel statebased on the received CSI-RS based on the feedback information. Althoughin FIG. 12 the UE includes the transceiver 1210 and the controller 1220,the UE may further include various components depending on functionsperformed thereon without limited thereto. For example, the UE mayfurther include a displaying unit displaying the current state of theUE, an input unit receiving signals such as performing functions fromthe user, and a storage unit storing data generated in the UE. Further,although the channel estimator 1230 is shown to be included in thecontroller 1220, it is not necessarily limited thereto. The controller1220 may control the transceiver 1210 to receive configurationinformation for each of at least one or more reference signal resourcesfrom the base station. Further, the controller 1220 may control thetransceiver 1210 to measure the at least one or more reference signalsand receive from the base station feedback configuration information togenerate feedback information based on the measurement result.

Further, the controller 1220 may measure at least one or more referencesignals received via the transceiver 1210 and generate feedbackinformation according to the feedback configuration information. Thecontroller 1220 may control the transceiver 1210 to transmit thegenerated feedback information to the base station at a feedback timingbased on the feedback configuration information. Further, the controller1220 may receive a channel status indication-reference signal (CSI-RS)from the base station, generate feedback information based on thereceived CSI-RS, and transmit the generated feedback information to thebase station. In this case, the controller 1220 may select eachprecoding matrix per antenna port group of the base station and furtherselect an additional precoding matrix based on the relationship betweenthe antenna port groups of the base station.

Further, the controller 1220 may receive a CSI-RS from the base station,generate feedback information based on the received CSI-RS, and transmitthe generated feedback information to the base station. In this case,the controller 1220 may select one precoding matrix for all the antennaport groups of the base station. Further, the controller 1220 mayreceive feedback configuration information from the base station,receive a CSI-RS from the base station, generate feedback informationbased on the received feedback configuration information and CSI-RS, andtransmit the generated feedback information to the base station. In thiscase, the controller 1220 may receive additional feedback configurationinformation based on the relationship between the antenna port groupsand the feedback configuration information corresponding to each antennaport group of the base station.

FIG. 13 is a block diagram illustrating a configuration of a basestation according to an embodiment of the present disclosure.

Referring to FIG. 13, the base station includes a controller 1310 and atransceiver 1320. The controller 1310 controls the state and operationof all the components of the base station to provide configurationinformation about the CSI-RS and feedback configuration information tothe UE and receive feedback information from the UE at a correspondingfeedback timing so that the UE may generate and transmit feedbackinformation based on at least one of the above-described embodiments ofthe present disclosure. Specifically, the controller 1310 allocatesCSI-RS resources to the UE for the channel estimation of the UE andallocates feedback resources and feedback timing to the UE. For this,the controller 1310 may further include a resource allocator 1330.Further, the base station allocates feedback configurations and feedbacktimings so that feedback transmissions from several UEs do not collidewith each other and receives and interprets the feedback informationconfigured at the corresponding timing. The transceiver 1320 performsthe function of communication data, reference signals, and feedbackinformation with the UE. Here, the transceiver 1320 transmits the CSI-RSto the UE through the allocated resource under the control of thecontroller 1310 and receives feedback information about the channelstate from the UE.

Further, although the resource allocator 1330 is shown to be included inthe controller 1310, it is not necessarily limited thereto. Thecontroller 1310 may control the transceiver 1320 to transmit theconfiguration information for each of at least one or more referencesignals to the UE or generate at least one or more reference signals.Further, the controller 1310 may control the transceiver 1320 totransmit to the UE feedback configuration information to generatefeedback information based on the measurement result. Further, thecontroller 1310 may control the transceiver 1320 to transmit the atleast one or more reference signals to the UE and receive the feedbackinformation transmitted from the UE at a feedback timing according tothe feedback configuration information. Further, the controller 1310 maytransmit the feedback configuration information to the UE, transmit theCSI-RS to the UE, and receive from the UE feedback information generatedbased on the feedback configuration information and the CSI-RS. In thiscase, the controller 1310 may transmit additional feedback configurationinformation based on the relationship between the antenna port groupsand the feedback configuration information corresponding to each antennaport group of the base station. Further, the controller 1310 maytransmit to the UE the beamformed CSI-RS based on the feedbackinformation and receive from the UE the feedback information generatedbased on the CSI-RS. According to the above-described embodiments of thepresent disclosure, it may be possible to prevent allocation ofexcessive feedback resources in transmitting CSI-RSs from the basestation using a number of two-dimensional antenna array transmitantennas and the increase in channel estimation complexity of the UE.The UE may effectively measure the channel of all of the many transmitantennas, configure the same in feedback information, and notify thesame to the base station.

1. A method for transmitting channel state information by a userequipment (UE) in a wireless communication system using multipleantennas, the method comprising: receiving control informationcomprising information associated with channel state reporting on asubband; receiving at least one reference signal and generating, basedon the at least one reference signal, periodic channel state informationcomprising a first precoding matrix indicator (PMI) for a wideband; andtransmitting the periodic channel state information comprising the firstPMI for the wideband based on the control information associated withchannel state reporting on the subband.
 2. The method of claim 1,wherein the control information denotes radio resource control (RRC)information, and wherein the RRC information further comprisesconfiguration information associated with the wireless communicationsystem using multiple antennas.
 3. The method of claim 1, wherein theinformation associated with channel state reporting on the subbandcomprises a period and an offset for channel quality indicator (CQI)reporting on the subband, and wherein a reporting time of the first PMIfor the wideband is set based on the period and the offset for the (CQI)reporting on the subband.
 4. The method of claim 1, wherein the periodicchannel state information further comprises a rank indicator (RI),wherein the information associated with channel state reporting on thesubband comprises a period and an offset for channel quality indicator(CQI) reporting on the subband, and wherein a reporting time of the RIis set based on the period and the offset for the CQI reporting on thesubband and a period and a relative offset for RI reporting.
 5. Themethod of claim 1, wherein the first PMI for the wideband is a PMIrelated to some bits of a PMI bit payload.
 6. The method of claim 1,wherein subsampling for the channel state reporting on the subbandcomprises subsampling a codebook by using codebook subsampling appliedto a predetermined number of transmit antennas.
 7. A user equipment (UE)in a wireless communication system using multiple antennas, the UEcomprising: a transceiver; and a controller couples with the transceiverand configured to: receive control information comprising informationassociated with channel state reporting on a subband; receive at leastone reference signal and generating, based on the at least one referencesignal, periodic channel state information comprising a first precodingmatrix indicator (PMI) for a wideband; and transmit the periodic channelstate information comprising the first PMI for the wideband based on thecontrol information associated with channel state reporting on thesubband.
 8. The UE of claim 7, wherein the control information denotesradio resource control (RRC) information, and wherein the RRCinformation further comprises configuration information associated withthe wireless communication system using multiple antennas.
 9. The UE ofclaim 7, wherein the information associated with channel state reportingon the subband comprises a period and an offset for channel qualityindicator (CQI) reporting on the subband, and wherein the controller isfurther configured to set a reporting time of the first PMI for thewideband, based on the period and the offset for the CQI reporting onthe subband.
 10. The UE of claim 7, wherein the periodic channel stateinformation further comprises a rank indicator (RI), wherein theinformation associated with channel state reporting on the subbandcomprises a period and an offset for channel quality indicator (COI)reporting on the subband, and wherein the controller is furtherconfigured to set a reporting time of the RI based on the period and theoffset for the COI reporting on the subband and a period and a relativeoffset for RI reporting.
 11. The UE of claim 7, wherein the first PMIfor the wideband is a PMI related to some bits of a PMI bit payload. 12.The UE of claim 7, wherein subsampling for the channel state reportingon the subband comprises subsampling a codebook by using codebooksubsampling applied to a predetermined number of transmit antennas. 13.A method for receiving channel state information by a base station in awireless communication system using multiple antennas, the methodcomprising: transmitting control information comprising informationassociated with channel state reporting on a subband; transmitting atleast one reference signal; and receiving periodic channel stateinformation, comprising a first precoding matrix indicator (PMI) for awideband, generated based on the at least one reference signal. 14.(canceled)
 15. (canceled)
 16. The method of claim 13, wherein thecontrol information denotes radio resource control (RRC) information,and wherein the RRC information further comprises configurationinformation associated with the wireless communication system usingmultiple antennas.
 17. The method of claim 13, wherein the informationassociated with channel state reporting on the subband comprises aperiod and an offset for channel quality indicator (CQI) reporting onthe subband, and wherein a reporting time of the first PMI for thewideband is set based on the period and the offset for the CQI reportingon the subband.
 18. The method of claim 13, wherein subsampling for thechannel state reporting on the subband comprises subsampling a codebookby using codebook subsampling applied to a predetermined number oftransmit antennas.
 19. A base station in a wireless communication systemusing multiple antennas, the base station comprising: a transceiver; anda controller coupled with the transceiver and configured to: transmitcontrol information comprising information associated with channel statereporting on a subband; transmit at least one reference signal; andreceive periodic channel state information, comprising a first precodingmatrix indicator (PMI) for a wideband, generated based on the at leastone reference signal.
 20. The base station of claim 19, wherein thecontrol information denotes radio resource control (RRC) information,and wherein the RRC information further comprises configurationinformation associated with the wireless communication system usingmultiple antennas.
 21. The base station of claim 19, wherein theinformation associated with channel state reporting on the subbandcomprises a period and an offset for channel quality indicator (CQI)reporting on the subband, and wherein a reporting time of the first PMIfor the wideband is set based on the period and the offset for the CQIreporting on the subband.
 22. The base station of claim 19, whereinsubsampling for the channel state reporting on the subband comprisessubsampling a codebook by using codebook subsampling applied to apredetermined number of transmit antennas.